This invention relates to a valve train for an engine and more particularly to an improved valve actuating system for an engine.
It has been recognized generally that the volumetric efficiency of an engine of a given displacement and bore diameter can be improved by utilizing a greater number of smaller dimension valves than a smaller number of larger dimension valves. For most practical purposes, in connection with automotive type engines, four valves per cylinder has regarded as the practical upward limit. There are a variety of reasons for this. One of the main reasons why engines have been generally limited to four valves per cylinder, even when high performance racing engines are employed, is that the incorporation of more than four valves per cylinder gives rise to certain design problems which can reduce the performance of the engine.
For example, if more than four valves per cylinder are employed with conventional arrangements, the surface area of the combustion chamber becomes quite large. This reduces performance due to excessive quenching. In addition, to provide adequate clearance, the clearance volume becomes relatively large and hence the compression ratio falls. This tends to reduce the performance. The use of more valves per cylinder than four can give rise to masking problems that can adversely effect the induction or exhaust efficiency.
Recently, it has been acknowledged that a certain specific placement of the valves and combustion chamber configuration will permit the use of five valves per cylinder and yet achieve high performance. The way this is normally done is to displace three intake valves and two exhaust valves, all at an acute angle to a plane containing the axis of the cylinder bore. The three intake valves are disposed so that two valves reciprocate along parallel axes that are at the same angle to this plane and the third valve reciprocates along an axis that is not parallel to the first and second axes and which lies at a different angle to the plane. However, such angular placement of the valves can give rise to difficulties in simplifying the actuation of the valves.
Coupled with the aforenoted problems, it is also desirable to provide in the valve actuating system a hydraulic lash adjuster so as to minimize servicing of the engine and to provide a more quiet running engine. However, coupled with the aforenoted problems, the positioning of the hydraulic lash adjusters for the engine further complicates the design.
It is, therefore a principal object of this invention to provide an improved multiple valve arrangement for an internal combustion engine that embodies hydraulic lash adjusters.
It is another object of the invention to provide a multiple valve engine having hydraulic lash adjusters in which the formation of the cylinder head can be relatively easy and at a low cost.